Radiation curable adhesive compositions and composite structures

ABSTRACT

This disclosure relates to novel adhesive compositions and composite structures utilizing the same, wherein said adhesive compositions contain an elastomer, a chemically compatible ethylenically unsaturated monomer, a tackifier, an adhesion promoter, and optionally, pigments, fillers, thickeners and flow control agents which are converted from the liquid to the solid state by exposure to high energy ionizing radiation such as electron beam. A particularly useful application for such adhesive compositions comprises the assembly of certain composite structures or laminates consisting of, for example, a fiber flocked rubber sheet and a metal base with the adhesive fulfilling the multiple functions of adhering the flocked fiber to the rubber sheet as well as adhering the rubber sheet to the metal base. Optionally, the rubber sheet itself may also be cured at the same time as the adhesive composition with all operations being carried out at ambient temperatures and in the presence of air, with exposure of said assembly to selected dosages of high energy ionizing radiation. These adhesive compositions contain no solvents thereby almost eliminating air pollution or solvent toxicity problems, and offer substantial savings in energy and labor as they are capable of curing in very short time periods without the use of external heat which might damage the substrate.

This is a division of application Ser. No. 045,863, filed June 6, 1979,now U.S. Pat. No. 4,319,942, issued Mar. 16, 1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains primarily to radiation curable adhesivecompositions and more particularly to high energy ionizing radiationcurable adhesive compositions containing no solvents, and theiremployment for the fabrication of certain composite structures.

2. Description of the Prior Art

The state of the art is believed to be indicated by the following citedreferences: U.S. Pat. No. 4,039,722--Dickie et al; U.S. Pat. No.3,938,566--Seiberling; U.S. Pat. No. 3,924,021--Maruyama et al; U.S.Pat. No. 3,869,341--Gotoda et al; U.S. Pat. No. 3,697,397--Kehr et al;U.S. Pat. No. 3,485,732--D'Alelio; U.S. Pat. No. 3,338,810--Warner; U.S.Pat. No. 3,188,229--Graham; and U.S. Pat. No. 2,921,006--Schmitz et al.

Basically, there are four main sources of radiant energy: gamma rays,high energy electrons, neutrons, and ultraviolet. Each of these sourceshas its respective advantages and disadvantages. The use of radiantenergy to cure polymeric coatings or adhesives is of fairly recentorigin, and it is only in the last several years that the two mostcommercially attractive sources, ultraviolet and electron beam, havebeen developed for use in industry. Because high energy radiation curingis a new technology, there are many shortcomings such as limitedproduction experience, high initial costs, and lack of coatings andadhesives adapted for use with ultraviolet or electron beam systems.Examples of typical ultraviolet applications include printing inks andcan coatings. These utilize polymeric materials such as acrylatedpolyethers, acrylated polyester-based polyurethanes, methacrylatedpolyesters and acrylated epoxies. With respect to electron beam, thereare only a few operations currently in use in this country with one ofthe largest being Ford Motor Company's Saline, Mich. plant which uses anelectron beam system to cure coatings on plastic parts, chieflydashboards.

Although both ultraviolet and electron beam systems require a blanket ofinert gas to eliminate the formation of harmful ozone gas, and have manyother similarities, an electron beam system differs from an ultravioletsystem in two main ways. First, an electron beam source delivers ahigher degree of penetration than an ultraviolet source. While thismakes possible the curing of coatings of significantly greaterthicknesses, an electron beam source requires a substantial capitalinvestment since equipment costs are high. An ultraviolet source, on theother hand, allows for less penetration, necessitating curing of onlythin layers of coating, but equipment costs are substantially lower.Second, compositions for UV curing require the presence of aphotosensitizer or photoinitiator, such as peroxide, benzoin orbenzophenone. The initiators add an estimated 15% to the cost ofultraviolet coatings as compared to electron beam coatings. Suchadditives are not required with an electron beam system thus resultingin less formulation work and reduced compound costs.

Electron beam curing systems also offer distinct advantages overconventional heat or chemical processing. Electron beam machinescurrently commercially available offer simple control of penetration,dose, and line speed. The usually rather compact machinery furthermoreallows for both uniform irradiation of a specific product as well as anintegrated processing capability in the presence of air, inert gases,etc. Single, multi-sample, or continuous conveyor feeds are available.

The basic chemistry of high energy ionizing radiation curing adhesivesor coatings involves free radical formation of certain reactive speciesdue to the radiant energy applied. Radiation intensity is, of course, afactor of prime importance. Reaction rate is a function of variablesother than radiation intensity such as temperature (the Arrheniusequation is applicable for correlating the temperature dependence of therate constant); concentration; location of double bonds; sterichindrance; resonance and inductive effects on the reactivity of thedouble bond; the size and molecular weight of the monomer; and theviscosity of the medium.

A wide variety of resins and monomers have been investigated for thehigh energy ionizing radiation curing of adhesives and coatings. Thesystems of greatest interest are based on a variety of polymerizableprepolymers and monomers. Polyesters and acrylics are the most common,but urethanes, alkyds, epoxies and silicones have likewise beeninvestigated, albeit to a lesser extent. Recently, a considerableresearch and development effort has been directed towards development ofradiation curable acrylic polymer and/or monomer systems. Acrylicmaterials have been prepared, for example, by converting vinylcopolymers of various monomers and glycidyl methacrylate to radiationcurable products by reacting the pendant oxirane group with acrylicacid. Acrylic derivatives have also been made based on modifyingurethanes and epoxy resins, including, for example, reaction ofappropriate polymeric moities with acrylyl chloride. The order ofreactivity to high energy ionizing radiation as determined by prior artresearch proposes that multifunctional acrylates are more reactive thanthe corresponding methacrylates. However, none of the prior art adhesiveor coating systems appear to be fully satisfactory for the preparationof such fiber flocked rubber and metal composite structures as thosedescribed herein.

To be most useful in radiation curing, adhesive compositions should haveminimum dose sensitivity. In simple terms, dose sensitivity means thatboth the total dosage and the rate of applied dosage affect the curerate. The desired non-dose sensitive adhesive systems will provide thesame cure results if the same radiation dosage is applied as tenexposures of one unit each, one exposure of ten units, or twentyexposures of a half unit each because a non-dose sensitive system isaffected by the total dosage only and is not affected by the size ofindividual doses administered.

It is a principal object of the present invention therefore to provide anew radiation curable adhesive composition for fabrication of certaincomposite structures.

It is also an object of the present invention to provide a new highenergy ionizing radiation curable adhesive composition which is not doserate sensitive and is curable at low total dosages for lowest cost.

It is a further object of the present invention to provide a newradiation curable adhesive composition capable of being cured byexposure to high energy ionizing radiation at ambient temperatures andin the presence of air for the fabrication of laminates consisting offiber flocked rubber sheets and a metal base.

It is another object of the present invention to provide a new radiationcurable adhesive composition comprised of specified blends ofelastomers, chemically compatible ethylenically unsaturated monomers,tackifiers, adhesion promoters and optionally, pigments, fillers,thickeners and flow control agents.

A still further object of the present invention is to provide a new highenergy ionizing radiation curable adhesive composition containing nosolvent thereby eliminating the need to remove the solvent from thecomposition as part of the curing process.

Other objects, features and advantages of the present invention willbecome apparent from the subsequent description, and examples, and theappended claims taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

In accordance with the present invention, an adhesive composition isprovided which is capable of being cured by high energy ionizingradiation and which comprises an elastomer, a chemically compatibleethylenically unsaturated polymerizable monomer or combination ofmonomers, a tackifier, an adhesion promoter, and optionally, pigments,fillers, thickeners and flow control agents. A particularly usefulapplication for such adhesive compositions comprises the assembly ofcertain composite structures or laminates consisting of, for example, afiber flocked rubber sheet and a metal base, with the adhesivefulfilling the multiple functions of adhering the flocked fiber to therubber sheet as well as adhering the rubber sheet to the metal base.Optionally, the rubber sheet itself may also be cured at the same timeas the adhesive composition with all operations being carried out atambient temperatures and in the presence of air, with exposure of saidassembly to selected dosages of high energy ionizing radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and others will be pointed out more fullyhereinafter in conjunction with the description of the preferredembodiment of the present invention illustrated in the accompanyingdrawings and examples and in which:

FIG. 1 is a cross-sectional view of an assembly line in which theadhesive composition of the present invention would be cured by highenergy ionizing radiation such as an electron beam.

FIG. 2 is a cross-sectional view of the adhesive composition of thepresent invention in use to adhere flock to a rubber substrate.

FIG. 3 is a cross-sectional view of the adhesive composition of thepresent invention in use to adhere flock to a rubber substrate, and toadhere the rubber substrate to a metal substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and are notfor the purpose of limiting the invention, FIG. 1 shows across-sectional view of an assembly line 10 in which a workpiece 20moves along conveyor 30 through high energy ionizing radiation such asan electron beam 40. The electron beam 40 is produced by an electronbeam emitting apparatus 50. The workpiece 20 would contain an electronbeam curing adhesive made in accordance with the present invention whichwould be cured after passing through electron beam 40.

FIG. 2 is a cross-sectional view of a laminate assembled by using thepresent invention. The laminate shown is comprised of a rubber strip 60of a thickness of about 1/8 inch, which is coated with about 2-5 mils ofan adhesive composition 70 made in accordance with the presentinvention. Into the adhesive composition 70 is deposited flock 80. Anyconventional method of flock deposition may be used, includingelectrostatic deposition.

FIG. 3 is a cross-sectional view of another laminate assembled by usingthe present invention. The laminate shown is in effect the laminatesection described in FIG. 2 attached to a metal strip 90 with about 2-5mils of the adhesive composition 70 of the present invention. Such alaminate is similar to that used in some types of automotiveweatherstripping wherein metal strips coated with rubber and flock areused to seal out water, air or dust at such locations as the door tomovable side window interface.

The adhesive composition of the present invention is comprised of twomajor components, an elastomer and a chemically compatible ethylenicallyunsaturated polymerizable monomer. The elastomeric base should bereactive with and be soluble in the monomer. Various elastomers possessthe necessary characteristics. A representative sample of suitableelastomers includes natural rubber, acrylonitrile butadiene rubber,polybutadiene rubber, polyisoprene rubber, Phillips Petroleum 414Cstyrene-butadiene rubber, neoprene WRT (a polychloroprene elastomermanufactured by DuPont), B. F. Goodrich Chemical Co. Hycar 1001(acrylonitrile butadiene type elastomer), PFA (a perfluoroalkoxy resinmanufactured by DuPont), ethylene-chlorotrifluoromethane copolymermanufactured by Allied Chemical Co. and marketed under the Halartradename, EA/AN/VTS (a terpolymer of ethyl acrylate, acrylonitrile, andvinyltrioxy silane prepared by Biorksten Research Lab of Madison, Wisc.)Kel-F fluorocarbon elastomer made by 3M Co., Monsanto Chemical Co. N5400(experimental acrylate), Thiokol Chemical Co. Thiokol ST polysulfideelastomers, and Dow Corning Corp. Silastic 250 organo-silicon polymer.Other suitable elastomers comparable or equivalent to those describedabove may also be used.

The chemically compatible unsaturated polymerizable monomer or monomersare liquid monomers such as styrene monomer or methyl acrylate monomer.Suitable styrene monomers are commercially supplied by Monsanto and DowChemical. When a blend of acrylonitrile and butadiene rubber is used asthe rubber base, an acrylate monomer such as ethyl acrylate, butylacrylate, methyl methacrylate, ethyl methacrylate, or butyl methacrylatesuch as those supplied commercially by Rohm & Haas or DuPont may beused. Also, difunctional acrylic monomers and trifunctional monomerssuch as ethylene glycol dimethacrylate, and trimethylpropanetrimethacrylate supplied by Sartomer Chemical Co. of West Chest, Pa. orWare Chemical Co. of Fairfield, Conn. may be used. Other suitablemonomers include vinyl toluene, diallylphthalate, triallylisocyanurate,triallylcyanurate, diallylmaleate, diallylsebacate, and vinylpyrrolidone. Still other suitable monomers comparable or equivalent tothose described above may also be used.

To improve the performance properties of the adhesive composition,various tackifiers and/or adhesion promoters may be added to the twomajor components described above. A tackifier resin such as Hercules,Inc. Piccolite LTP 135 or Piccotex (both modified resin derivatives), orRohm & Haas Amberol may be used. Piccolite LTP 135 resins comprisephenolic-modified terpene resins; Piccotex resins comprise copolymers ofvinyltoluene and alpha-methylstyrene monomers; and Amberol comprisesmaleic-resin and resin-modified and unmodified phenolformaldehyde-typepolymers. Depending upon the type of substrates to be bonded together aswell as the speed of curing desired, four different types of adhesionpromoters may be used: one, variously substituted silanes includingvinyl silanes such as Union Carbide Corp. A172 or A174 or aminosilanessuch as Union Carbide Corp. A179; two, metal salts of selected longchain acids such as cobalt naphenate or cobalt octonate; three,methacrylic and/or acrylic acids and their esters; and four,hydroxyalkylacrylates and/or methacrylates such as hydroxypropylmethacrylate or hydroxyethylmethacrylate and/orhydroxypropylmethacrylate.

Other materials that may be added to the adhesive composition of thepresent invention include pigments such as conventional inorganic and/ororganic pigments. Inorganic pigments including lead chromate, molybdenumcompounds, iron oxide, titanium oxide, zinc oxide, etc. and/or organicpigments including phthalocyanines, carbon black, quinacridones,perylene colors, anthraquinones, thioindigo reds, etc. are believed tobe suitable. In addition, fillers such as any conventional inorganicmineral filler, e.g., silicas, aluminas, magnesia, titanium dioxide,molybdenic oxide, etc. may be used. Flow control agents or thickenerssuch as Cab-O-Sil finely divided silica made by Cabot Corp. or Santorel,also a finely divided silica, made by Monsanto may likewise be used.

With regard to curing a layer of rubber simultaneously with the adhesivecomposition of the present invention, any rubber capable of being curedwith a sulfur or peroxide type recipe is believed to be satisfactory.This would preferably include rubbers with vinyl or alkyl unsaturation.

With regard to suitable sources of high energy ionizing radiation, ithas been found that an electron beam accelerator such as a 11/2 MEVDynamitron or a 3 MEV Dynamitron made by Radiation Dynamics, Inc., ofPlainview, Long Island, N.Y. are satisfactory. Other electron beammachines are made by High Voltage Engineering Co. or Energy SciencesCo., both of Massachusetts. Another possible source of high energyionizing radiation is cobalt 60 isotope radiation.

Although the adhesive composition of the present invention as describedabove will perform satisfactorily, it has surprisingly been found thatthe following ranges may be used to obtain optimum performance.

    ______________________________________                                                   Broad                                                                         Range                Most                                                     (weight     Preferred                                                                              Preferred                                     Component  percent)    Range    Range                                         ______________________________________                                        (a)   elastomer                                                                              10 to 80    15 to 40                                                                             20 to 40                                    (b)   monomer  90 to 10    60 to 30                                                                             50 to 40                                    (c)   tackifier                                                                               2 to 20     5 to 15                                                                              8 to 12                                    (d)   adhesion 0.2 to 10   3 to 6 4 to 5                                            promoter                                                                ______________________________________                                    

EXAMPLE 1

An exemplary formulation of a preferred embodiment of the presentinvention which has been found to provide excellent performanceproperties is given below:

    ______________________________________                                                                 Amount                                               Ingredient               by Weight                                            ______________________________________                                        Phillips 414C styrene-butadiene rubber base                                                            137.5                                                Monsanto styrene monomer 501.0                                                Hercules, Inc. Piccolite LTP 135 tackifier                                                             70.0                                                 Union Carbide A 179 amino-silane mixture                                                               9.9                                                  (10% silane, 90% styrene-monomer)                                             Rohm & Haas methacrylic acid                                                                           7.3                                                  Witco Chemical cobalt naphthenate                                                                      0.137                                                ______________________________________                                    

EXAMPLE 2

The following procedure was followed in an effort to evaluate theperformance of the adhesive composition described in Example 1 of thepresent invention:

(1) Approximately 2 to 5 mils of the adhesive composition of Example 1was applied to the top of a piece of plain steel.

(2) A piece of styrene-butadiene rubber, about 1/8 inch thick was thenpressed onto the adhesive with finger pressure.

(3) Approximately 2 to 5 mils of the adhesive composition of Example 1was applied to the top of the rubber.

(4) Polyester flock (3 denier×0.030 inch) was then applied to theadhesive using an electrostatic process of flock deposition.

(5) This laminate was then subjected to an electron beam dosage of about15 mrads at Radiation Dynamics, Inc. in Plainview, Long Island, N.Y.,using a 1.5 MEV Machine for this 1/8 inch thickness of rubber. (A 3.0MEV Machine would be used for a 1/4 inch thickness of rubber.)

(6) Several test specimens were returned to the laboratory to test the180° peel adhesion strength of the flock to the rubber substrate. Theintegrity of this adhesive bond between the flock and the substrateaffects the wear characteristics of the end products, and thus is usedas a standard test to evaluate the performance of flock adhesives.

(7) The test specimens containing the electron beam cured adhesive ofExample 1 exhibited 180° peel adhesion strength values of between about10 to 15 pounds per inch (ppi), when pulled apart at 12 inches perminute, with 6 ppi being the acceptable minimum value.

(8) Test specimens containing a typically used heat cured adhesive weretested as a control and were found to exhibit 180° peel adhesionstrength values of between about 10 to 15 ppi. Adhesion strength valuesfor a comparable heat cured peroxide adhesive system would be about 10to 15% lower.

From the above test results it should be noted that the radiation curedadhesive composition of the present invention performed at least as wellas a typically used heat cured adhesive composition. Due to the factthat the adhesive composition of the present invention also offers manyadvantages over prior art adhesives for such applications, it isbelieved that it will be very attractive to many manufacturers. Some ofthese advantages are described in the following paragraphs.

Although the preferred embodiment of the adhesive composition of thepresent invention as described in Examples 1 and 2, provides excellentadhesion to plain steel, it should be noted that similar performance canbe expected on electrogalvanized or adhesive-primed steels. In addition,test results have shown that both nylon and cotton flocks can be used ina composite assembly similar to that described in Example 2, therebyincreasing the versatility and adaptability of the present invention.

Due to the fact that the adhesive composition of the present inventionis 100% solids with no solvents present, it presents several advantages.First, since the energy requirements of radiation curing units aresubstantially lower than those of the baking ovens used to evaporatesolvents and promote thermal cures which they replace, there is reducedenergy consumption. Second, since the adhesive is completely convertedto a plastic-like film when cured, nothing is discharged into theatmosphere, thus resulting in a virtual elimination of air pollution.Third, with the adhesive composition being composed of 100% solids, andthus no flow-out of adhesive after application, there is less chance oftoxicity. All of the above advantages are especially important today toall those industries affected by recent environmental and healthlegislation.

In addition to the advantages described above, the present inventionalso provides a rapid curing adhesive system in which cross-linking ofthe polymer adhesive occurs almost instantaneously, thus allowing forhigh line speeds. In addition, since radiation curing systems areextremely compact compared to conventional production baking ovens,there is an effective utilization of plant space. Also, since curing ofthe adhesive composition occurs at or near room temperature withaccompanying energy savings, there is minimal substrate heating and thusthe resulting ability to cure on temperature sensitive substrateswithout the fear of incinerating the substrate.

The adhesive compositions of the present invention have also been foundto present the economic benefits of lower cost and greater pricestability. Typically, a free radical initiator such as peroxide, benzoinor benezophenone presents significant additional material cost inproportion to its percentage in the adhesive formulation, is oftensubject to shortages, and usually presents storage stability problems.Since radiation beam curing processes do not require such an initiator,the above problems are avoided.

While it will be apparent that the preferred embodiment of the inventiondisclosed is well calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation, change, and substitution of equivalents without departingfrom the proper scope or fair meaning of the subjoined claims.

What is claimed is:
 1. An adhesive composition capable of being cured byhigh energy ionizing radiation comprising:between about 10 to about 80percent of a material with elastomeric properties which comprises atleast one material selected from the group consisting of natural rubber;acrylonitrile-butadiene rubber; polybutadiene rubber; polyisoprenerubber; styrene-butadiene rubber; polychloroprene elastomer;perfluoroalkoxy resin; ethylene-chlorotrifluoromethane copolymer;terpolymer of ethyl acrylate, acrylonitrile and vinyltrioxy silane;fluorocarbon elastomer; polysulfide elastomer; and organo-siliconpolymer; between about 90 to about 10 percent of an ethylenicallyunsaturated polymerizable monomer which comprises at least one materialselected from the group consisting of styrene, methyl acrylate, ethylacrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, ethylene glycol dimethacrylate, trimethylpropanetrimethacrylate, vinyl toluene, diallylphthalate, triallylisocyanurate,triallylcyanurate, diallylmaleate, diallylsebacate, and vinylpyrrolidone; between about 2 to about 20 percent of a tackifier whichcomprises at least one material selected from the group consisting ofphenolic-modified terpene resins, copolymers of vinyltoluene andalpha-methylstyrene monomers, and maleic-resin and resin-modified andunmodified phenolformaldehyde-type polymers; and between about 0.2 toabout 10 percent of an adhesion promoter which comprises at least onematerial selected from the group consisting of variously substitutedsilanes, metal salts of long chain acids, methacrylic or acrylic acidsand their esters, and hydroxyalkylacrylates or methacrylates.
 2. Theadhesive composition of claim 1 wherein said adhesive compositionfurther comprises a pigment selected from the group consisting of leadchromate, molybdenum compounds, iron oxide, titanium oxide, zinc oxide,phthalocyanines, carbon black, quinacridones, perylene colors,anthraquinones, and thioindigo reds.
 3. The adhesive composition ofclaim 1 wherein said adhesive composition further comprises a fillerselected from the group consisting of silicas, aluminas, magnesia,titanium dioxide, and molybdenic oxide.
 4. The adhesive composition ofclaim 1 wherein said adhesive composition further comprises a flowcontrol agent or thickener comprising finely divided silicas.
 5. Anadhesive composition capable of being cured by high energy ionizingradiation, for use on a rubber substrate, wherein said adhesioncomposition comprises:between about 10 to about 80 percent of a materialwith elastomeric properties which comprises at least one materialselected from the group consisting of natural rubber;acrylonitrile-butadiene rubber; polybutadiene rubber; polyisoprenerubber; styrene-butadiene rubber; polychloroprene elastomer;perfluoroalkoxy resin; ethylene-chlorotrifluoromethane copolymer;terpolymer of ethyl acrylate, acrylonitrile and vinyltrioxy silane;fluorocarbon elastomer; polysulfide elastomer; and organo-siliconpolymer; between about 90 to about 10 percent of an ethylenicallyunsaturated polymerizable monomer which comprises at least one materialselected from the group consisting of styrene, methyl acrylate, ethylacrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, ethylene glycol dimethacrylate, trimethylpropanetrimethacrylate, vinyl toluene, diallylphthalate, triallylisocyanurate,triallylcyanurate, diallylmaleate, diallylsebacate, and vinylpyrrolidone; between about 2 to about 20 percent of a tackifier whichcomprises at least one material selected from the group consisting ofphenolic-modified terpene resins, copolymers of vinyltoluene andalpha-methystyrene monomers, and maleic-resin and resin-modified andunmodified phenolformaldehyde-type polymers; between about 0.2 to about10 percent of an adhesion promoter which comprises at least one materialselected from the group consisting of variously substituted silanes,metal salts of long chain acids, methacrylic or acrylic acids and theiresters, and hydroxyalkylacrylates or methacrylates; a pigment whichcomprises at least one material selected from the group consisting oflead chromate, molybdenum compounds iron oxide, titanium oxide, zincoxide, phthalocyanines, carbon black, quinacridones, perylene colors,anthraquinones, and thioindigo reds; a filler which comprises at leastone material selected from the group consisting of silicas, aluminas,magnesia, titanium dioxide, and molybdenic oxide; and a flow controlagent or thickener comprising finely divided silicas.
 6. An adhesivecomposition capable of being cured by high energy ionizing radiation,for use in bonding rubber to metal, wherein said adhesive compositioncomprises from about 10 to about 80 percent of a styrene-butadienerubber base, from about 90 to about 10 percent of a styrene monomer,from about 2 to about 20 percent of a tackifier which comprises at leastone material selected from the group consisting of phenolic-modifiedterpene resins, copolymers of vinyltoluene and alpha-methystyrenemonomers, and maleic-resin and resin-modified and unmodifiedphenolformaldehyde-type polymers, and from about 0.2 to about 10 percentof an adhesion promoter comprising an amino-silane mixture of about 10%silane and about 90% styrene monomer, methacrylic acid, and cobaltnaphthenate.
 7. The adhesive composition of claim 1 wherein,part (a) ispresent from about 15 to about 40 percent, part (b) is present fromabout 60 to about 30 percent, part (c) is present from about 5 to about15 percent, and part (d) is present from about 3 to about 6 percent. 8.The adhesive composition of claim 1 wherein,part (a) is present fromabout 20 to about 40 percent, part (b) is present from about 50 to about40 percent, part (c) is present from about 8 to about 12 percent, andpart (d) is present from about 4 to about 5 percent.